1. Field of the Invention
The present invention relates to sharpening devices, and in particular to a device for clamping a circular saw blade for sharpening.
2. Description of the Prior Art
In order to maximize the usage of circular saw blades, the cutting edges of their teeth must be periodically resharpened. For proper cutting, each tooth should have the same clearance, hook angle, slope from front to back, rake, and height. Circular saw blades with teeth having excessive variance among these characteristics, even though sharp, tend to leave jagged kerfs, draw to one side or the other, cut unevenly and may even be dangerous to a user.
Although specialized machinery has been devised for grinding saw blades to precise specifications, for example at their place of manufacture, such equipment is relatively complex and expensive and thus impractical for the worker desirous of sharpening only a relatively small quantity of saw blades. For example, many workers find it expedient to sharpen their own saw blades and possibly those of a crew with which they work. Although not as accurate as specialized machine tools, hand tools such as ordinary files can give satisfactory results, particularly where a saw blade merely requires "touching up".
A common problem encountered in sharpening saw blades by hand lies in the necessity of securely clamping the blade in a fixed position so that accurate sharpening can be accomplished manually. A relatively simple method of clamping a saw blade for sharpening involves placing it in an ordinary vice with opposing jaws which are threadably drawn together against opposite sides of the blade. The prior art is replete with other clamping devices utilizing screw-type actuators. For example, both the Winkler Pat. No. 333,092 and the Dominiak Pat. No. 2,130,076 patents show devices with a pair of jaws for threadably clamping against a circular saw blade.
In a typical manual sharpening operation, a circular saw blade is rotated nearly 360 degrees throughout the operation so that the teeth to be sharpened are facing in a desired direction for convenient access thereto. Ideally the saw blade would be rotated as each tooth was sharpened a distance equal to the circumferential spacing of the teeth whereby each would be in exactly the same position relative to the operator when sharpened. However, clamping devices with jaws which are threadably drawn together, such as many of those shown in the prior art, consume relatively large amounts of time in merely tightening and untightening motions. For the sake of expediency when using such threadably actuated clamping devices, the saw blade is often left in the same position while a number of teeth are sharpened. The results generally suffer somewhat when this procedure is followed because the file orientation varies from tooth to tooth and hence the shapes to which the teeth are manually filed tend to be somewhat inconsistent.
A second disadvantage with not rotating the saw blade each time a different tooth is filed is that whatever light source is employed for the operation will cause sutble differences in the appearance of saw teeth with different orientations. The operator is thus hampered in visually guaging the configuration to which each tooth is filed for purposes of maintaining consistency.
To relieve the tediousness associated with tightening and untightening a screw-type mechanism each time the saw blade is rotated, saw blade clamps have been devised which employ springs for urging the jaws of a clamp together. Such devices are exemplified by the Russel Pat. No. 985,209 and Willard Pat. No. 2,707,888 patents. However, both of these mechanisms utilize levers which must be manually engaged and pivoted to release positions before the blade can be rotated. Even though preferable to threadably actuated clamps, these structures tended to delay an operator in releasing the clamp.